1. Field of the Invention
The present invention relates to a sense-amplifier control circuit for a current-sensing sense amplifier that performs voltage sensing after current sensing and a controlling method of the sense amplifier.
2. Description of the Related Art
In recent years, low voltage operation has been demanded for semiconductor devices. In addition, stable, low voltage operation has been demanded for sense amplifiers used for fetching data from a memory-cell array such as a DRAM and a flash memory. High speed operation is also needed for some sense amplifiers used for certain purposes.
For example, Japanese Patent Application Publication No. 2000-285161 proposes a current-sensing sense amplifier that supports a low-voltage operation.
However, the sense-amplifier control circuit disclosed in Japanese Patent Application Publication No. 2000-285161 suffers from certain drawbacks recognized by the present inventors. With some kinds of configurations of sense-amplifier control circuits, the transition from the current sensing to the voltage sensing occurs while the current sensing has not been executed sufficiently. In this case, if the state of an initial voltage of an output terminal is not normal, and an operation error may occur, that is, the output logic may become opposite to the proper logic. A longer current-sensing period to avoid the occurrence of operation errors causes a problem such as making high-speed operation difficult.
A current-sensing sense amplifier with an equalizing function has been proposed for the purpose of reducing the occurrence of operation errors. In this kind of a sense amplifier, the initial voltages of the output terminals are equalized and then the current sensing is performed. Accordingly, the occurrence of the operation errors caused by an abnormal initial voltage can be reduced. There may be, however, cases in which the equalization (pre-charging) is insufficient. Accordingly, it is still possible that the above-described operation errors occur.